1979 Chrysler 7.5hp 72h9b absolutely refuses to run.

Motor sat for 10 years and was given to me for free.

Motor won't run for more than 5 seconds. Acting like a 2 stroke that's starved of fuel. Motor has new fuel tank, new fuel lines, new fuel pump, and a carb that has been completely disassembled and rebuilt about 6 times. Compression and spark are good. I have the fuel bulb sitting vertical with the arrows pointing in the right direction.

I'm a very experienced garage mechanic, I've rebuilt dozens of carbs, but this is my first boat motor. I've been trying to get this thing to run for 2 days
and I'm about to give up. I'm hoping someone more experienced in the field can point me in a direction I've overlooked.

My current thoughts are perhaps the float isn't set right, but I can't find a spec anywhere. Only adjustment screw I can find is the idle adjust. Is there a way to test the fuel pump?

How to set the float.
The carb upside down, the float needs to be level.
The drop should almost touch the side of the post.
The idle screw controls the air/fuel at idle.
Start with the screw at 1 1/2 turns out.
Then adjust from there.

Adjusting the air/fuel. Should be done in the water in gear.
Start the motor, initial setting, Most motors 1 1/2 turn from lightly seated.
Some need the screw set at 2-3 turns out, you'll have to trial and error to figure that out.
As the motor runs, turn the screw in 1/8th turn wait 10 seconds and then you can turn in another 1/8th
Very important to wait 10 seconds to burn the gas at that setting.
Repeat until the motor bucks, kicks, backfires any change, then turn back out 1/2 turn.

The screw holding the bowl on is the main jet.
Make sure the holes are clear or it will just burn the fuel in the bowl and not do anything more.

Spark tester, hook up 2 to the plug leads.
Start the motor and watch the fire as it runs then dies.

ANY???? blow back from the carb? inspect the reeds.